Any parent will tell you that there is no simple recipe for raising a child. Being a parent means getting hefty doses of advice - often unsolicited - from others. But such advice often fails to consider a critical factor: the child. A new review of dozens of studies involving more than 14,600 pairs of twins shows that children's genetics significantly affect how they are parented.
"There is a lot of pressure on parents these days to produce children that excel in everything, socially and academically," says Reut Avinun of the Hebrew University of Jerusalem. "Since children are not born tabula rasa, I felt it was important to explore their side of the story, to show how they can affect their environment, and specifically parental behavior." Most studies of parenting look at only the reverse, how parents affect their children's experiences.
To explore the flip side, Avinun and Ariel Knafo looked to twins. They reasoned that if parents treat identical twins, who share 100 percent of their genes, more similarly than non-identical twins, who share on average 50 percent of their genes, then it suggests that the child's genes shape parenting.
Indeed, across 32 studies of twins, they found that children's genetically-influenced characteristics do affect parental behavior. As published in Personality and Social Psychology Review, they estimated that 23 percent of differences in parenting is due to a child's genetics. The genotype-related differences are ways that the children evoke different responses from their environment. For example, a child that is antisocial is more likely to elicit harsh discipline from parents than a more social child.
In one recent study, Knafo's research group found that boys with less self-control are more likely to experience lower levels of positive maternal behavior. For boys, but not for girls, a particular genotype - a polymorphic region in the gene that codes for the serotonin transporter - predicted mothers' levels of positive parenting and the boys' level of self-control. "In other words, boys' genetically influenced level of self-control affected the behavior of their mothers toward them," Avinun says.
Avinun and Knafo also found that children's shared environment - socioeconomics, cultural exposure, etc. - accounts for 43 percent of parenting differences. And the non-shared environment - different schools, friends, etc. - accounts for 34 percent of the differences. Importantly, the study's findings support the idea that parenting does not necessarily affect children in the same family similarly.
Several factors affect the extent to which genetics influence parenting. Avinun and Knafo found, for example, that age was important, supporting the argument that the child's genetic influence on parenting increases with age. "As children become increasingly autonomous, their genetic tendencies are more likely to be able to affect their behavior, which in turn influences parental behavior," Avinun says.
The research in total, Avinun says, "means that parenting should not be viewed solely as a characteristic of the parent, but as something that results from both parental and child attributes." Therefore, any interventions or treatments to help parenting should consider both the parents and children, and could vary even within a family.
"The discussion of 'nature vs. nurture' has transformed into 'nature and nurture.' We now understand that most characteristics are determined by the interplay between genetic and environmental influences," Avinun says.
Because children are born differently, there never can be a general rule book for raising children, she explains. "There isn't one style of ideal parenting. Each child requires a different environment to excel. So parents should not invest a lot of effort in trying to treat their children similarly, but instead, be aware of the variation in their children's attributes and nurture them accordingly."